[SPARK-3841] [mllib] Pretty-print params for ML examples

Provide a parent class for the Params case classes used in many MLlib examples, where the parent class pretty-prints the case class fields:
Param1Name	Param1Value
Param2Name	Param2Value
...
Using this class will make it easier to print test settings to logs.

Also, updated DecisionTreeRunner to print a little more info.

CC: mengxr

Author: Joseph K. Bradley <joseph.kurata.bradley@gmail.com>

Closes #2700 from jkbradley/dtrunner-update and squashes the following commits:

cff873f [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
7a08ae4 [Joseph K. Bradley] code review comment updates
b4d2043 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
d8228a7 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
0fc9c64 [Joseph K. Bradley] Added abstract TestParams class for mllib example parameters
12b7798 [Joseph K. Bradley] Added abstract class TestParams for pretty-printing Params values
5f84f03 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
f7441b6 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
19eb6fc [Joseph K. Bradley] Updated DecisionTreeRunner to print training time.